Fact
Potted plants without plates underneath and overwatering are the main reasons for causing stains on walls.
While placing plants on windows, balconies or terraces, one must always invest in plates or trays to collect the excess water. During summers, this excess water can also help birds to quench their thirst. However, we recommend to keep the trays clean periodically of this water to avoid breeding of any insects or pests.
Second, avoid flood irrigation or pouring large amounts of water in one go. It will not only save you from creating those ugly stains but will also from eroding nutrients from the soil.